In cellular telephony systems, the area covered by the system is, as the name implies, divided into cells. Usually, the cells are divided along a more or less radial direction, extending from a centre point where a base station and an antenna associated with the base station is located.
A user in the system will adaptively be assigned to one or a few of the cells of the system, usually the cell or cells for which the user's telephone experiences the best signal quality, typically defined by the signal strength or signal-to-interference-plus-noise ratio, S/(I+N), of a broadcast reference signal, for example a pilot signal in a CDMA system. The adaptivity means that the user is “handed over” from one cell to another depending on the signal quality of the broadcast reference signals corresponding to the respective cells.
The cells are thus defined by the coverage of the base station antenna or antennas in terms of a quality measure such a signal strength or S/(I+N). Near the site of the base station, where the borders of the cells converge, there will be a plurality of borders close to each other, which may lead to very frequent and rapid handovers, which is not desirable, as this may lead to reductions in communication quality, and in some cases even to dropped telephone calls.